1. Field of the Invention
The present invention relates to a load measuring device for pulling up a monocrystalline rod that is being grown by the Czochralski method (CZ method) using a strain gauge.
2. Description of the Prior Art
In the Czochralski single crystal growth technology, it is known to automatically control the crystal diameter using the sectional area or diameter at the interface between a melt and the monocrystalline rod which is computed from an increment of a crystal's weight, or to control the position of the surface of the melt relative to a heater by moving a crucible up by the computed shift deducted from the pulled-up weight increment.
Such controls employ devices for measuring a pulling-up load of a monocrystal rod which incorporates a load cell.
However, if a load cell with a wire resistance strain gauge incorporated is used to detect the load of the monocrystalline rod that is being lifted by a wire rope, a lot of continuous wave-shaped noise is often detected, which is the cause of detection errors and thereby worsens practical use of the load cell. Use of a load cell has therefore been conventionally limited to a single crystal growth apparatus in which a monocrystalline rod is lifted by a shaft. This also applies to a load cell which employs a strain gauge of a type other than the wire resistance type strain gauge.
The pulling shaft is moved up and down several meters in accordance with a required pulling-up stroke, and this results in a technically or economically unbearable increase in the overall size of the single crystal growth apparatus.